linux-kernel - [PATCH] mm/dmapool.c: micro-optimisation remove unnecessary branch

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Message-Id: <20200320173317.26408-1-mateusznosek0@gmail.com>
Date:   Fri, 20 Mar 2020 18:33:17 +0100
From:   mateusznosek0@...il.com
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Mateusz Nosek <mateusznosek0@...il.com>, akpm@...ux-foundation.org
Subject: [PATCH] mm/dmapool.c: micro-optimisation remove unnecessary branch

From: Mateusz Nosek <mateusznosek0@...il.com>

Previously there was a check if 'size' is aligned to 'align' and if not
then it was aligned. This check was expensive as both branch and division
are expensive instructions in most architectures.
'ALIGN' function on already aligned value will not change it, and as it is
cheaper than branch + division it can be executed all the time and
branch can be removed.

Signed-off-by: Mateusz Nosek <mateusznosek0@...il.com>
---
 mm/dmapool.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index fe5d33060415..f9fb9bbd733e 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -144,9 +144,7 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
 	else if (size < 4)
 		size = 4;
 
-	if ((size % align) != 0)
-		size = ALIGN(size, align);
-
+	size = ALIGN(size, align);
 	allocation = max_t(size_t, size, PAGE_SIZE);
 
 	if (!boundary)
-- 
2.17.1